Fuel system for fuel injected internal combustion engines

ABSTRACT

A method of operating a fuel system having a fuel pump (15) to supply fuel to a fuel metering apparatus (23) operable to provide metered quantities of fuel for injection to an engine, and an electronic controller (22) responsive to a plurality of input signals to determine the engine fuel demand and to control the activation of the fuel metering apparatus ( 23 ) to deliver a quantity of fuel to meet said fuel demand. The method comprising maintaining a fuel supply to said fuel metering apparatus (23) within predetermined fuel pressure or fuel level parameters, and cyclically operating said fuel pump-to maintain said fuel supply within said parameters. Further providing a signal from the sensor (18) to an electronic controller (23) indicative of the pressure of the fuel supply at the fuel metering apparatus (23) as one of said input signals to be processed by the electronic controller (23) in the control of the fuel metering apparatus (22). The accuracy of the fuel metering is thereby not adversely affected by the intermittent operation of the pump (  15 ). The pump ( 15 ) preferably provides fuel to a closed chamber that acts in the manner of an accumulator (16), and a pressure sensor (18) provides an input signal to the electronic controller (22) indicative of the pressure of the fuel available to the fuel metering apparatus (23) from the accumulator (16). Alternatively the chamber may maintain the fuel between predetermined levels at a substantially steady or variable pressure.

This invention relates to a fuel system for delivering meteredquantities of fuel to an internal combustion engine and is particularlyapplicable to fuel systems incorporating a fuel injector which candeliver fuel either directly to the engine combustion chamber or to theair induction system of the engine.

It is customary to provide in a fuel injection system a fuel pressureregulator to maintain the fuel supply at a preset pressure, as thepressure of the fuel is relevant to the process of motoring the fuel tothe engine. Where a conventional pressure regulator is used, it isnecessary to provide a fuel return line from the regulator to the fuelreservoir, thus effectively doubling the length of fuel line between thefuel reservoir and the fuel injection equipment that convey fuel at highpressure. The increase in fuel line length represents an expense in boththe supply of material and assembly thereof, and also significantlyincreases the risk of high pressure fuel leakage developing.

From the point of view of safety, and also economy, it is desirable toreduce the extent of fuel lines between the fuel reservoir and theengine. This is particularly so in marine engine installations whereleaked fuel can collect in an enclosed area and present a major firehazard.

More importantly the energy consumed in pumping fuel at a ratesubstantially in excess of the engine fuel requirement represents asignificant energy waste. Currently the fuel pump in a fuel injectionsystem is normally electrically driven and operates continuously, thusconsumes substantial electrical energy circulating fuel that is notrequired. This energy waste particularly occurs during low to mediumload and/or speed operation of the engine and as the energy to drive thefuel pump is supplied directly or indirectly from the engine, energywasted in pumping excess fuel represents a significant component of thefuel consumption of the engine.

There has been proposed such as in U.S. Pat. Nos. 3,967,598 and4,565,173, fuel injection systems wherein the fuel pump is operatedcyclically so as to maintain a substantially constant fuel supplypressure to the injector, and also so as to avoid the necessity ofproviding a return fuel circuit from the pump to the fuel tank orreservoir.

In both of these proposals, the fuel pump is required to operate at aduty cycle, directly related to the injection frequency, which in turnis related to engine speed. A pump operating on a duty cycle of suchhigh frequency inherently has a low pumping efficiency, and consequentlya low energy consumption efficiency. Further, the operation of a pump ina high frequency cycling mode severely reduces the life of the pump.

Although the fuel system proposed in U.S. Pat. No. 3,967,598 doesprovide an accumulator downstream of the fuel pump, the pump is stillrequired to operate on a cyclic basis at a frequency equal to thefrequency of injection. The accumulator is only provided for the purposeof attempting to substantially maintain the designed pressure for thesupply of fuel to the injector and to overcome mechanical and hydraulicinduced time delays which would otherwise prevent the attaining ofsubstantial synchronism between the injector cycle and the pump cycle.

It is the object of the present invention to provide a method andapparatus for the supply of fuel to an engine which enables themaintenance of accurate metering of the fuel to the engine in accordancewith the engine fuel demand, avoids the necessity of a high pressurefuel return line to the fuel reservoir and improve the operationalefficiency of the fuel pump.

With this object in view there is provided according to the presentinvention a method of operating a fuel system supplying meteredquantities of fuel for delivery to an internal combustion engine, saidsystem having a cyclically operable fuel pump, a metering means toreceive fuel supplied by the pump, and a processor to control themetering means to deliver a metered quantity of fuel to the engine, saidprocessor determining the metered quantity of fuel required by theengine in response to signal inputs thereto indicating engine operatingconditions, said method including intermittently operating said pumpunder control by the processor to maintain a fuel supply to the meteringmeans at a pressure between selected limits, said limits being selectedso that the pump means delivers during each period of operation aquantity of fuel greater than a multiple of the maximum single meteredquantity of fuel deliverable by the metering means, and sensing thepressure of the fuel supply to the metering means, and inputting to theprocessor a signal indicative of the sensed pressure, said processorapplying said fuel pressure signal in the control of the metering meansto deliver the required quantity of fuel.

Conveniently the fuel is supplied by the pump to a chamber, preferably aclosed chamber, from which the fuel is directly supplied to the fuelmetering means. The chamber may act in the manner of an accumulator, anda pressure sensor provides the input signal to the processor indicativeof the pressure of the fuel available to fuel metering means from theaccumulator.

The processor can be adapted to control the operation of the fuel pumpin accordance with the pressure input signal so that the pressure of thefuel in the accumulator is maintained between the selected maximum andminimum pressures. Alternatively, the cycling of the pump may becontrolled by an input signal to the processor indicative of the fuellevel in the chamber or by a fuel level sensor directly controlling theoperation of the pump.

It will be appreciated that the pressure of the fuel supplied to thefuel metering means will influence the rate of delivery of the fuel bythe metering means such as the rate of flow of the fuel through ametering orifice. Thus the processor is required to take account of thepressure of the fuel supply in the control of the quantity of fueldelivered to the engine. Normally the fuel metering means includes aselectively opening port or nozzle and the period of opening of thenozzle or port is varied to control the amount of fuel delivered. Thus avariation in the pressure drop across the nozzle or port will influencethe rate of fuel flow when the port or nozzle is opened, and theprocessor can control that period in accordance with the pressure of thefuel supplied to the port or nozzle together with other engine operatingconditions to achieve delivery of the correct amount of fuel. The fuelpressure sensor may alternatively be arranged to sense the pressuredifferential between the fuel supply and a gas into which the fuel isdelivered during metering. This input can similarly be used by theprocessor in achieving accurate metering of the fuel.

The above fuel supply system has the advantage that no pressurised fuelreturn line is required from the high pressure side of the pump, and thepump is only operated to meet the actual fuel demand of the engine, thusrepresenting a substantial saving in energy which would normally be usedmerely to pump fuel from the reservoir which was subsequently returnedto the reservoir. Further as the processor receivers an input indicationthe actual pressure of the fuel supply to the fuel metering means it isnot necessary to maintain the fuel supply pressure substantiallyconstant. Accordingly the fuel pump can be operated on a non-regularintermittent basis with substantial time intervals between successiveoperating periods. The pump can thus operate at the designed speed athigh efficiency and low overall energy consumption and reduced wearrate.

In addition, by having a sensor to deliver a signal to the processor toindicate the actual pressure of fuel available to the fuel meteringmeans, no pressure regulation is required and the processor alone canaccurately control the fuel metering means to ensure the correct fuelquantity is delivered to the engine to meet the fuel demand thereof atall fuel supply pressures.

Currently there are in use fuel injection systems wherein the meteredquantity of fuel is delivered to the engine entrained in a gas, usuallyair. In such injection systems it is common to effect the metering ofthe fuel as it is delivered into the gas and thus the pressure of thegas is relevant to the fuel metering process. Accordingly, when the fuelsupply pump is intermittently operated, to control the pressure of thefuel supply to the fuel metering means, the processor may be arranged tovary the pressure of the fuel supply in response to variations in thepressure of the gas into which the fuel is metered to control thepressure differential therebetween. Thus a substantially constantpressure differential can be maintained between the fuel and gas.Alternatively the pressure differential between the fuel and the gas canbe sensed and controlled to achieve the substantially constant pressuredifferential.

Also it is desirable under some engine operating conditions to vary thepressure of injection of the fuel or fuel - gas mixture to the engine.This can be achieved with the presently proposed fuel supply system dueto the ability to vary the fuel supply pressure without adverselyaffecting the fuel metering process.

There is also provided according to the present invention a fuel systemfor an internal combustion engine, said system comprising a fuel pumpfor delivering fuel from a fuel reservoir to a fuel metering means,including an intermediate reservoir downstream of the fuel pump, sensormeans to generate a signal indicative of the pressure of the fuel in theintermediate reservoir, and a processor to receive and process saidsignal to maintain said pressure of the fuel in the intermediatereservoir within predetermined limits by selectively switching the fuelpump on and off. Preferably the processor also responds to the pressureof the fuel supply in the intermediate reservoir in the control of thefuel metering means to meet said fuel demand, whereby the accuracy ofthe fuel metering is not adversely affected by the cycling of theoperation of the pump.

The invention will be more readily understood from the followingdescription of one practical arrangement of the fuel system asillustrated in the accompanying drawing.

FIG. 1 is a schematic representation of the fuel system particularlyapplicable to marine engines.

Referring now to FIG. 1, the plurality of fuel metering and injectordevices 10 are arranged so that each device delivers fuel to arespective cylinder or cylinder inlet port of a multi-cylinder engine.It is to be understood that the number of fuel metering and injectordevices will vary with the character of the fuel system and there may bea single device even for a multi-cylinder engine.

Each of the fuel metering and injector devices 10 receive fuel from acommon fuel rail 11 which is supplied with fuel from the fuel reservoir12. As the installation shown is for use in marine applications, thefuel reservoir 12 in turn receives fuel from the remote fuel tank 13 viathe lift pump 14. The fuel reservoir 12 is fitted with a float valve 9which will close to prevent the delivery of fuel by the lift pump 14when the fuel level in the reservoir 12 has reached a preset level. Theprovision of the fuel reservoir 12, lift pump 14 and float valve 9 arefor the purposes of complying with U.S. regulations relating to marineengines. These regulations do not apply in other installations such asautomobiles or other motor vehicles, in which installations the fuelreservoir 12 would be the conventional fuel tank of the vehicle.

The high pressure fuel pump 15 draws fuel from the reservoir 12 anddelivers it to the accumulator 16 via the fuel filter 17. Theaccumulator 16 is in the form of a closed chamber having at least onedeflectable or movable wall 19 which is preloaded by the spring 20 orthe like resilient component. The wall 19 is displaced or deflectedupwardly as viewed in FIG. 1 by the pressure of the fuel and as fuel isdelivered to the accumulator and downward by the spring as fuel iswithdrawn. Thus the pressure of the fuel in the accumulator can bemaintained within preset limits while fuel is being delivered therefromto the fuel rail 11 and hence to the metering and injector units 10. Theaccumulator 16 may alternatively be constructed to maintain a nearsteady pressure of the fuel therein with the fuel level moving betweenset upper and lower levels with a position sensor to issue a signal toindicate the fuel level.

The pressure sensor 18 is responsive to the pressure of the fuel in theaccumulator 16 or anywhere upstream thereof and down stream of theinjector devices 10, and generates a signal for input to the ECU 22which is programmed to switch the pump 15 on and off so as to maintainthe pressure in the accumulator 16 between preset maximum and minimumvalues. Thus when the rate of fuel consumption is low the pump will beswitched off for long periods until sufficient fuel is consumed from theaccumulator to allow the pressure to drop from the maximum to theminimum preset value. Even at maximum fuel consumption rates, theoperation of the fuel pump 15 will be cycled on and off as the capacityof the accumulator is selected to be a multiple of the maximum fuelconsumption rate per cycle of the injector system. It will beappreciated that a similar cycling of the pump operation will beobtained by the ECU 22 receiving signals from position sensorsindicating the fuel level such as level sensor 26 in the accumulator.The capacity of the accumulator and the permitted variation in fuelpressure or fuel level therein is preferably selected is that, even atmaximum fuel consumption rate, the pump is switched on at intervalscorresponding to 50 or more fuel deliveries by the injectors. The on andoff cycling of the fuel pump will provide a substantial reduction inenergy consumption by the fuel system, particularly consumption ofenergy in the form of electrical power generated by an alternator drivenby the engine. This saving is particularly significant when the engineis operating at low to medium loads and/or speeds.

The signal input to the ECU 22 by the pressure sensor 18 is also used inthe control of the fuel metering component 23 of the fuel metering andinjector devices 10 so that in determining the amount of fuel requiredeach fuel delivery event, account will be taken of the actual fuelpressure at that point in time. This enables the accurate calculation ofthe required period of opening of the fuel metering component to deliverthe quantity of fuel calculated to meet the fuel demand of the engine.

The ECU also receives the conventional inputs for determination of theengine fuel demand such as engine speed, engine bad and enginetemperature.

As the fuel pump 15 only operates when fuel is required to maintain thefuel supply within the preset pressure or level limits, it is notnecessary to provide a return line from the fuel rail 11 to thereservoir 12. However, for other reasons, such as to ensure against theaccumulation of fuel vapour in the fuel rail 11, having regard to thetemperature of the environment in which the fuel rail is located, it canbe desirable in some installations to provide for the bleeding of asmall amount of fuel back from the fuel rail to the reservoir 12. Thiscan be achieved by providing an appropriate return line 21 whichincorporates a flow control orifice 24 selected so that the amount offuel returned to the reservoir 12 is only that sufficient to preventvapour accumulating in the rail 11. A solenoid actuated valve may beprovided in the return line 21 which is opened under the control of theECU 22 in accordance with a preset cycle or in response to operatingconditions such as engine temperature, start-up conditions or fueltemperature.

The above described method and apparatus for supplying fuel to an engineis applicable to fuel injection systems wherein fuel alone or fuel andgas such as air are delivered to the engine, including fuel injectorsystems wherein the metered quantity of fuel is entrained in air priorto or during injection. A typical construction of such a fuel meteringand injection system is disclosed in U.S. Pat. No. 4,934,329 thedisclosure of which is incorporated herein by reference.

In a fuel injection system wherein the fuel is metered into air to becarried thereby to the engine, the ECU 22 can also receive an inputsignal indicative of the pressure of that air to be used in controllingthe fuel metering. Also air at that pressure, which may tosub-atmospheric, can be applied to the movable wall 19 of theaccumulator 16 to complement the load applied by the spring 20. In thisarrangement the pressure of the fuel in the accumulator will be relatedto the air pressure in a preset manner. This is beneficial in the fuelmetering operation in that a substantially steady pressure differentialcan be achieved between the fuel and air supplies. It can also bedesirable to increase the gas pressure at high load operation of theengine relative to the pressure at low to medium load conditions, or inrelation to engine speed either alone or in combination with engineload. The processor can be arranged to determine when such a gaspressure charge is to be effected by input signals indicating engineload and/or speed or in response to the fuel requirement of the enginebeing above a predetermined level.

I claim:
 1. A method of operating a fuel system supplying meteredquantities of fuel for delivery to an internal combustion engine, saidsystem having a cyclically operable fuel pump, a metering means toreceive fuel supplied by the pump, and a processor to control themetering means to deliver a metered quantity of fuel to the engine, saidprocessor determining the metered quantity of fuel required by theengine in response to signal inputs thereto indicating engine operatingconditions, said method including intermittently operating said pumpunder control of the processor to maintain a fuel supply to the meteringmeans at a pressure between selected limits, said limits being selectedso that the pump delivers during each period of operation a quantity offuel greater than a multiple of the maximum single metered quantity offuel deliverable by the metering means, sensing the pressure of the fuelsupply to the metering means, and inputting to the processor a signalindicative of the sensed pressure, said processor applying said fuelpressure signal in the control of the metering means to deliver therequired quantity of fuel.
 2. A method of operating a fuel system asclaimed in claim 1 wherein the processor also applies said fuel pressuresignal in the control of the intermittent operation of the pump tomaintain the fuel pressure within said limits.
 3. A method of operatinga fuel system as claimed in claim 2, wherein the fuel pump delivers thefuel to an accumulator.
 4. A method of operating a fuel system asclaimed in claim 1 wherein the fuel pump delivers fuel to anaccumulator, and the intermittent operation of the pump is controlled inresponse to predetermined variations in the pressure of the fuel in theaccumulator.
 5. A method of operating a fuel system as claimed in claim4 including sensing the pressure of the fuel in the accumulator, andinputting to the processor a signal indicative of said sensed fuelpressure, said processor applying said signal in the control of theintermittent operation of the pump.
 6. A method of operating a fuelsystem as claimed in claim 1 wherein the metering means delivers themetered quantity of fuel into a gas charge, and said sensing of thepressure of the fuel is determined by reference to the pressuredifferential between the fuel and said gas charge.
 7. A method ofoperating a fuel system supplying metered quantities of fuel fordelivery to an internal combustion engine, said system having acyclically operable fuel pump, a metering means to receive fuel suppliedby the pump and a processor to control the metering means to deliver ametered quantity of fuel into a gas charge delivered to the engine, saidprocessor determining the metered quantity of fuel required by theengine in response to signal inputs thereto indicating engine operatingconditions, said method including intermittently operating said pumpunder control of the processor to maintain a fuel supply to the meteringmeans at a pressure between selected limits, said limits being selectedso that the pump delivers during each period of operation a quantity offuel greater than a multiple of the maximum single metered quantity offuel deliverable by the metering means, sensing the pressure of the fuelsupply to the metering means by reference to a pressure differentialbetween the fuel and said gas charge, inputting to the processor asignal indicative of the sensed pressure, said processor applying saidfuel pressure signal in the control of the metering means to deliver therequired quantity of fuel, and controlling the pressure of the gascharge by said processor to vary said gas charge pressure in response topredetermined changes in engine load and/or speed.
 8. A method asclaimed in claim 7 wherein the processor increases the gas chargepressure when the engine fuel requirement is above a predeterminedlevel.
 9. A fuel system for an internal combustion engine, said systemcomprising a fuel pump for delivering fuel from a fuel reservoir to afuel metering means, including an intermediate reservoir downstream ofthe fuel pump and located between the fuel pump and the fuel meteringmeans, sensor means to generate a signal indicative of the pressure ofthe fuel in the intermediate reservoir, and a processor to receive andprocess said signal to maintain said pressure of the fuel in theintermediate reservoir within predetermined limits by selectively andintermittently switching the fuel pump on and off to deliver during eachperiod of operation a quantity of fuel greater than a multiple of themaximum single metered quantity of fuel deliverable by the meteringmeans.
 10. A fuel system for an internal combustion engine, said systemcomprising a fuel pump for delivering fuel from a fuel reservoir to afuel rail in communication with a fuel metering means, including anintermediate reservoir downstream of the fuel pump and located betweenthe fuel pump and said fuel rail, sensor means to generate a signalindicative of the pressure of the fuel in the intermediate reservoir,and a processor to receive and process said signal to maintain saidpressure of the fuel in the intermediate reservoir within predeterminedlimits by selectively switching the fuel pump on and off.
 11. The methodof operating a fuel system as claimed in claim 3, wherein fuel passesthrough an accumulator located between the fuel pump and the fuelmetering means.
 12. The method of operating a fuel system as claimed inclaim 3, wherein fuel passes through an accumulator located between thefuel pump and a fuel rail in communication with said metering means. 13.The method of operating a fuel system as claimed in claim 3 wherein theaccumulator stores during each period of pump operation said quantity offuel greater than a multiple of the maximum single metered quantity offuel deliverable by the metering means.
 14. A fuel system for aninternal combustion engine, said system comprising a fuel pump fordelivering fuel from a fuel reservoir to a fuel metering means,including an intermediate reservoir downstream of the fuel pump, sensormeans to generate a signal indicative of the pressure of the fuel in theintermediate reservoir, and a processor to receive and process saidsignal to maintain said pressure of the fuel in the intermediatereservoir within predetermined limits by selectively and intermittentlyswitching the fuel pump on and off to deliver during each period ofoperation a quantity of fuel greater than a multiple of the maximumsingle metered quantity of fuel deliverable by the metering means.
 15. Afuel system as claimed in claim 9 wherein the processor is arranged toprocess said signal indicative of the pressure of the fuel in theintermediate reservoir in the control of the fuel metering means todeliver the quantity of fuel to meet the engine fuel demand.
 16. Thefuel system as claimed in claim 14 wherein the intermediate reservoirstores during each period of pump operation a quantity of fuel greaterthan a multiple of a maximum single metered quantity of fuel deliverableby the fuel metering means.
 17. A method of operating a fuel system asclaimed in claim 1, wherein the fuel pump delivers fuel to anaccumulator, and the intermittent operation of the pump is controlled inresponse to predetermined variations in the level of the fuel in theaccumulator.
 18. A method of operating a fuel system as claimed in claim17 including sensing the level of the fuel in the accumulator, andinputting to the processor a signal indicative of the sensed fuel level,said processor applying said signal in the control of the intermittentoperation of the pump.